RESTRICTIONS IN THE REPERTOIRE OF ALLOSPECIFIC T-CELLS - CONTRIBUTIONOF THE ALPHA-HELICAL SEQUENCE POLYMORPHISM OF HLA-DR MOLECULES

We have studied the molecular diversity of the allogeneic TCR repertoi re specific for the HLA-DR4 variant, DRB10404, by analyzing the Vbeta gene segment usage of CD4+ T cell clones from nine different donors a nd comparing the Vbeta repertoire in allospecific and unselected T cel l populations. To investigate the forces shaping the repertoire of the alloreactive T cell response we compared the diversity of TCR specifi cities utilized in very similar and in disparate responder/stimulator combinations. Six of the responders shared the HLA-DRB10401 allele, w hich differs from the HLA-DRB10404 allele by only two amino acid subs titutions at positions 71 and 86 of the HLA-DRbeta1 chain; three respo nders expressed HLA-DRB1 alleles with extensive polymorphisms compared with the stimulator HLA-DRB1 allele. In all nine responders, TCR spec ificities recruited to recognize HLA-DRB10404 were strongly biased to ward the dominant usage of one to three Vbeta elements. Despite some d egree of heterogeneity between different responders, the overall patte rn was very similar with a hierarchy of TCR Vbeta elements expressed b y HLA-DRB10404 specific T cells. A core group of Vbeta elements (Vbet a6, 5, 2, 13.2, 18, and 7) was preferentially used, whereas other Vbet a elements including Vbeta3, 4, and 8 were infrequently used or not us ed at all. Sequencing of the VDJbeta region from selected T cell clone s showed no junctional bias associated with the preferential Vbeta gen e segment usage. Surprisingly, the T cell diversity in focused and in complex alloreactive responses were equally biased. The finding that H LA-DR4+ and DR4- donors exhibited a similar bias supports the interpre tation that the alpha-helical HLA-DR structure of the stimulator cell has a dominant contribution in shaping the alloreactive repertoire.